FIELD FIELD-OFFSET FILE-BLOCK
FIELD
* FIELD ( offset size "name" -- offset+size )

create a field - the workhorse for both >STRUCT and >STRUCTURE
implementations. The created fieldname is an OFFSET:-word
that memorizes the current offset in its PFA and will add
that offset on runtime. This forth-word does *not* align. 
 : FIELD CREATE
   OVER ,
   +
 DOES>
    @ +
 ;

struct defining primitive